Hi - after troubleshooting all night, here is how I was able to finally succeed in sending a 3 page fax (most faxes would typically fail on page 1 or in the middle of page 2).
I read many posts suggesting setting the baud rate to 9600 with error correction turned off, but had no success with these settings. It seems after reading many posts on this subject, that there is some debate on the speed to use and whether or not error correction should be disabled. In my case, here is what worked (finally!).
Fax machine: HP Officejet J4680 All-in-One
Service: Callcentric
Speed: 14400
Error Correction: On (enabled)
Most importantly, I used a dsl filter plugged directly into the OBI (fax line going into the filter port labeled "phone"). I read this suggestion on another site, and sure enough it worked.
Hope this helps.